1. Field of the Invention
The invention relates to a method and apparatus for optically inspecting tubular products. More specifically the invention is used for non-destructive periodic inspection of pressure containing heat transfer tubes.
2. Description of the Prior Art
Successful and reliable performance of pressure containing tubular products often requires periodic non-destructive inspection to monitor tubing conditions and ultimately provide the basis for a rational maintenance and repair strategy. In the power generation industry, a number of inspection techniques are used to assess the condition of tubular products used in a wide variety of applications. Often a number of techniques are used to complement each other because of the inherent advantages and limitations associated with virtually all tests. For example, slower yet more descriptive ultrasonic test methods are often used to complement higher speed less quantitative eddy current methods in heat transfer tubing applications. Optical inspection is an important test which offers good credibility. However, optical inspection is rarely practical except in extreme circumstances. Detailed visual inspections are very time consuming, and image interpretation can be difficult under in service conditions even using the most advanced equipment.
Ultra high resolution charged coupled device (CCD) video probe cameras combined with image processing computer capability offer the promise of both rapid and automatic visual examination of tubular products. In reality, however, image processing of in service tubing inspection data is very difficult because of the typical wide variation in range of features and image quality encountered during the visual scan of even a single tube. In many applications, miles of tubing must be examined.
Until the present invention, the promise of rapid and automatic visual inspection has not been realized. In the present invention, visual information may be collected using a technique which complements existing inspection methods. The method provides detailed information yet permits relatively fast inspection of tubing products in the order of one foot per second.